Harrison does not explain what the excessive demands were, but the letter reveals they had more say over their affairs than the generations of boy bands that followed in their wake.

The letter will also be a surprise to Beatles fans as they believe that the band's long standing producer George Martin was the only person they ever worked with until they split in 1970.

Instead it seems they seriously thought about working with Jim Stewart at Stax in Memphis at the same time they were recording 'Revolver'.

The result would have been potentially fascinating as Stewart had produced hits from singers like Otis Redding.

The handwritten letter was sent on May 7 1966 by Harrison to Atlanta DJ Paul Drew and thanked him for sending him some records.

At the end he wrote: 'P.S. Did you hear that we nearly recorded in Memphis with Jim Stewart.

'We would all like it a lot, but too many people get insane with money ideas at the mention of the word 'Beatles,' and so it fell through!'

The letter was last week sold by Los Angeles-based rock collectables dealer Jeff Gold for £13,000.

He told Rolling Stone: 'When I read the Stax part I was like: 'What the hell is this?'

'I spent an inordinate amount of time thinking about this stuff, and I knew it was a major revelation.'

The letter also reveals what Harrison thinks of where the band is at in the early stages of recording Revolver.

He also seemed to understand that Capitol Records were planning the release of Yesterday and Today, their 1966 US-only album.

Harrison wrote: 'The album we are making now (Revolver) should be out around October.

'But I hear Capitol will make an intermediate album (Yesterday and Today) with unused tracks from Rubber Soul, a few old singles and about two or three of the new tracks we have just cut ... Well I am off to the studio any minute, as soon as John and Ringo arrive.'

Gold said that the accepted wisdom was that Capitol 'did pretty much whatever they wanted with Beatles records', but Harrison's letter suggests otherwise.

He said: 'To see that George had a very specific understanding of what Yesterday and Today was going to be before it came out was kind of a revelation too. It surprised me.'